   "Yields the next state of the board."
   [board]
   (vec (map step-row (window (repeat nil) board))))
+
+;; compare indexed-step the index-free:
+(- (nth (iterate indexed-step glider) 8)
+   (nth (iterate index-free-step glider) 8))
+;;=> true or should be:
+
 
 (defn step 
  "Yields the next state of the world"

  ([pad coll]
   (partition 3 1 (concat [pad] coll [pad]))))

(defn cell-block 
  "Creates a sequences of 3x3 windows from a triple of 3 sequences."
  [[left mid right]]
  (window (map vector left mid right))) 

(defn liveness
  "Returns the liveness (nil or :on) of the center cell for
   the next step."  

      3 :on
      nil)))

;; the new idexed-step function depending on index free helper functions:
(defn- step-row
  "Yields the next state of the center row."
  [rows-triple]
